1. Field of the Invention
The present invention relates to a battery pack, and more particularly, the present invention relates to a battery pack having an improved electrical coupling structure between a bare cell and a protection circuit module.
2. Description of the Related Art
Recently, compact and lightweight portable electronic devices, such as cellular telephones, notebook computers and camcorders, etc., have been actively developed and produced. The portable electronic devices include a built-in battery pack so as to be operated at locations where external power sources are unavailable. The battery pack includes a secondary battery that can be charged or discharged.
The secondary battery can be a nickel-cadmium (Ni—Cd) battery, a nickel-hydrogen (Ni—MH) battery, a lithium (Li) battery and a lithium ion (Li-ion) secondary battery, etc. Particularly, the lithium ion secondary battery has an operating voltage that is three times that of the nickel-cadmium (Ni—Cd) battery or the nickel-hydrogen (Ni—MH) battery that are usually used as a power supply of the portable electronic devices. In addition, the lithium ion secondary battery has been widely used because it has higher energy density per unit weight.
The secondary battery uses lithium group oxides as a cathode active material, and a carbonic material as an anode active material. The secondary battery is divided into a liquid electrolyte battery and a polymer electrolyte battery according to the kind of electrolyte used. A lithium ion battery uses a liquid electrolyte, and a lithium polymer battery uses a polymer electrolyte.
The secondary battery is formed by sealing a bare cell in a can containing an electrode assembly and electrolyte and then electrically coupling the bare cell to a protection circuit module. The bare cell is charged or discharged electricity through a chemical reaction and the protection circuit module protects the bare cell by controlling charge/discharge of the bare cell and preventing overcharge/overdischarge thereof.
In a conventional battery, the bare cell and protection circuit module are electrically and mechanically coupled to each other through a welding or soldering process. In other words, an electrode terminal and a lead plate of the protection circuit module are connected to each other by welding or soldering and then the lead plate is welded or soldered to the electrode terminal of the bare cell.
Accordingly, the welding or soldering process is performed several times in assembling the bare cell and protection circuit module. Thus, it takes a great deal of time and the process is difficult.
Particularly, the welding or soldering process are not suitable for high precision that is required due to the recent trend to slim the battery.